1. Field of the Invention
This invention relates to generally to a method and apparatus for manipulating needle-like medical instruments such as performing ultrasound guided needle biopsies and similar ultrasound guided procedures.
2. Discussion of the Related Art
Needle-like instruments are often used in medical procedures, and must be manipulated accurately. For example, in a needle biopsy, the needle has to be inserted into an anatomical target to remove a tissue sample. Ultrasound guidance is routinely used for example, when performing breast needle biopsies. The real time ultrasound images allow the physician to locate the target and to monitor the needle position. An example of a typical ultrasound imaging apparatus is disclosed in U.S. Pat. No. 5,503,152, entitled ULTRASOUND TRANSDUCER ASSEMBLY AND METHOD FOR THREE DIMENSIONAL IMAGING, issued on Apr. 2, 1996 to Oakley, et al.
The biopsy procedure is usually performed within the projected ultrasound image plane. With the ultrasound transducer being in a position where the target is visible in the displayed ultrasound image, the insertion point of the needle is ideally chosen so that the point resides along a line residing at the intersection of the projected ultrasound plane and the patient""s skin surface. The needle is then preferably oriented so that it lies within this plane and points towards the target. When the needle is inserted it will appear in the ultrasound image, and the progress of the needle along a path towards the target can be visually monitored.
One difficulty inherent with performing an ultrasound guided needle biopsy is to correctly position and orient the needle so that the needle resides within the same plane as the displayed ultrasound image. Mechanical needle guides are commercially available to facilitate this task. They are clipped onto the transducer and constrain the movement of the needle so that it is forced to stay in a plane aligned with the transducer. Examples of such mechanical guides are disclosed in U.S. Pat. No. 5,076,279 entitled NEEDLE GUIDE FOR ASSEMBLY UPON AN ULTRASOUND IMAGING TRANSDUCER, issued to Arenson et al. on Dec. 31, 1991 and U.S. Pat. No. 6,475,152 entitled BIOPSY NEEDLE GUIDE FOR ATTACHMENT TO AN ULTRASOUND TRANSDUCER, issued on Nov. 5, 2002 to Kelly, Jr. et al. Even though the needle can be reliably placed in the plane of the ultrasound image, many physicians find the rigid constraint imposed by the use of a mechanical guide bothersome and consequently do not use one. Physicians typically want to be able to make corrective adjustments to the path of the needle as it approaches the target, which is not easily achieved with the constraints of the mechanical needle guide. In addition, because a mechanical guide constrains the needle entry point to be close to the transducer, it is not possible to insert the needle at the distance from the transducer, as is required for shallow needle angles.
Whether or not the physician is utilizing a mechanical guide, she must look away from the patient at the ultrasound image display and manipulate the needle without direct reference to either her hand or the target. This causes an unnatural eye hand coordination problem that creates additional complications for the physician performing the procedure. Ideally, the physician would be able to look directly at the desired path and destination point of the needle, but the opacity of the human body normally prevents such a view.
One technology that provides a simulated view inside the body during the performance of a needle biopsy is Real Time Tomographic Reflection. A discussion of this technique is provided in REAL TIME TOMOGRAPHIC REFLECTION: PHANTOMS FOR CALIBRATION AND BIOPSY by George Stetten et al., Proceedings IEEE and ACM International Symposium on Augmented Reality, 29-30 October 2001, N.Y. City, N.Y., pages 11-19. In this technique, the ultrasound image is visually merged with the normal exterior view of the patient. The physician""s hands and the needle appear in the physician""s natural field of view while the biopsy is being performed.
A guide according to principles of the present invention utilizes a light beam or video camera as a guide for placing the needle in the ultrasound plane. In one embodiment, the present invention includes an optical guide for a needle-like instrument comprising an ultrasonic transducer that projects a planar ultrasound beam into an imaging plane beneath a surface and a source of illumination, aligned with the ultrasonic transducer. The source of illumination projects a light beam onto the surface, the light beam being coplanar with the imaging plane. A viewing device, displays an image produced by the ultrasonic transducer which appears to be superimposed on the surface while the light beam is visible on the surface. The line of light on the patient""s skin marks the intersection of the ultrasound plane with the patient""s skin surface and hence marks the location of possible in-plane entry points for the needle. The user places the tip of the needle on the line of light projected onto the skin. Then the needle is oriented. When the needle is aligned in an in-plane pose, the needle is seen to be illuminated by the light along its length. The image displayed on the viewing device provides guidance to adjust the tilt of the needle within the ultrasound plane towards the target.
In a different embodiment of the present invention, the light beam is replaced by a video camera. An apparatus for video assisted guidance of a biopsy needle comprises means for projecting an ultrasonic imaging plane beneath a surface, means for creating a video image of the surface, and means for inserting graphic markers on the video image of the surface. The inserted graphic markers are substantially coplanar with the ultrasonic imaging plane. By looking at the image, the physician may place the needle on the skin along the superimposed line, and then orient the needle to be co-linear with the line. The viewing device generates a composite image containing the image produced by the ultrasonic transducer and the image of the surface along with the graphic markers.